1. Field
The following description relates to a level shifter, and, for example, to a level shifter having a single power source.
2. Description of Related Art
In a system on chip (SOC) in which a circuit system formed of combinations of various types of semiconductor circuits is realized in a chip form, a block requiring a high performance uses a high voltage, and a block requiring a low performance uses a low voltage to save energy. Since the blocks use different types of voltages, a leakage current may increase or problems may occur in functions of the blocks in an interface section between the blocks.
In order to solve this problem, a level shifter, which converts a voltage supplied from an external source into a high level voltage or a low level voltage, is used as an interface circuit to change a voltage level between the blocks.
FIG. 1 is a circuit diagram illustrating a conventional level shifter. Referring to FIG. 1, the conventional level shifter receives an input signal in having a relatively low level voltage vdd and performs level shifting with respect to the input signal in to output an output signal out having a relatively high level voltage vdda. For example, if the input signal in has the high level voltage vdd, transistors MN1 and MP2 are respectively turned on, thereby outputting the output signal out having the high level voltage vdda. If the input signal in has a low level voltage vss, transistors MN2 and MP1 are respectively turned on, thereby outputting an output signal having a low level voltage vss.
However, since these transistors are to apply additional power to inverters that are to invert an input signal, the number of power pins increases, thereby increasing the number of pins. Therefore, manufacturing cost of a level shifter increases, and a design of the level shifter is increasingly complicated.